1,793 research outputs found
A broadband radio study of the average profile and giant pulses from PSR B1821-24A
We present the results of wide-band (720-2400 MHz) study of PSR B1821-24A
(J1824-2452A, M28A), an energetic millisecond pulsar visible in radio, X-rays
and gamma-rays. In radio, the pulsar has a complex average profile which spans
>85% of the spin period and exhibits strong evolution with observing frequency.
For the first time we measure phase-resolved polarization properties and
spectral indices of radio emission throughout almost all of the on-pulse
window. We combine this knowledge with the high-energy information to compare
M28A to other known gamma-ray millisecond pulsars and to speculate that M28A's
radio emission originates in multiple regions within its magnetosphere (i.e.
both in the slot or outer gaps near the light cylinder and at lower altitudes
above the polar cap). M28A is one of the handful of pulsars which are known to
emit Giant Pulses (GPs) -- short, bright radio pulses of unknown nature. We
report a drop in the linear polarization of the average profile in both windows
of GP generation and also a `W'-shaped absorption feature (resembling a double
notch), partly overlapping with one of the GP windows. The GPs themselves have
broadband spectra consisting of multiple patches with fractional spectral width
() of about 0.07. Although our time resolution was not
sufficient to resolve the GP structure on the microsecond scale, we argue that
GPs from this pulsar most closely resemble the GPs from the main pulse of the
Crab pulsar, which consist of a series of narrowband nanoshots.Comment: 16 pages, 8 figures, accepted to Ap
Executive Function Differences In Medicated Depressed, Non-Medicated Depressed, And Non-Medicated Non-Depressed Individuals
The purpose of the current study was to assess the performance of depressed young adults on tests of executive function, while addressing the variables of age and medication status, which have been inconsistently measured in previous research. It was hypothesized that statistically significant group differences would occur on tests of executive functions in three distinct groups: medicated depressed, non-medicated depressed, and non-medicated non-depressed individuals.
Participants included 53 adults who were medicated depressed ( n = 15), non-medicated depressed (n = 16), and non-medicated non-depressed (n = 22) and were between the ages of 19 and 40 years. Participants completed measures assessing depression, psychological well-being (including anxiety), intelligence, and executive functions.
Between group comparisons revealed several statistically significant differences on executive function measures including the Wisconsin Card Sorting Test (WCST) Trials Administered, WCST Failure to Maintain Set, Trail Making Test (TMT) B, Stroop Word, Stroop Color, Stroop Color-Word, and Stroop Interference. The non-medicated non-depressed group performed better overall than those in the non-medicated depressed and medicated depressed groups. Post hoc stepwise regression analyses indicated that anxiety predicted performance on a number of executive function measures to a greater degree than did depression.
Findings suggest that executive functions of young adults are affected by depression, medication status, and anxiety. Results of the present study contradict the assumption that psychotropic medications do not affect cognitive abilities. These findings also suggest that future research investigating the interaction between anxiety and executive functions are necessary
Discovery of an Energetic Pulsar Associated with SNR G76.9+1.0
We report the discovery of PSR J2022+3842, a 24 ms radio and X-ray pulsar in
the supernova remnant G76.9+1.0, in observations with the Chandra X-ray
telescope, the Robert C. Byrd Green Bank Radio Telescope, and the Rossi X-ray
Timing Explorer (RXTE). The pulsar's spin-down rate implies a rotation-powered
luminosity Edot = 1.2 x 10^{38} erg/s, a surface dipole magnetic field strength
B_s = 1.0 x 10^{12} G, and a characteristic age of 8.9 kyr. PSR J2022+3842 is
thus the second-most energetic Galactic pulsar known, after the Crab, as well
as the most rapidly-rotating young, radio-bright pulsar known. The radio
pulsations are highly dispersed and broadened by interstellar scattering, and
we find that a large (delta-f / f ~= 1.9 x 10^{-6}) spin glitch must have
occurred between our discovery and confirmation observations. The X-ray pulses
are narrow (0.06 cycles FWHM) and visible up to 20 keV, consistent with
magnetospheric emission from a rotation-powered pulsar. The Chandra X-ray image
identifies the pulsar with a hard, unresolved source at the midpoint of the
double-lobed radio morphology of SNR G76.9+1.0 and embedded within faint,
compact X-ray nebulosity. The spatial relationship of the X-ray and radio
emissions is remarkably similar to extended structure seen around the Vela
pulsar. The combined Chandra and RXTE pulsar spectrum is well-fitted by an
absorbed power-law model with column density N_H = (1.7\pm0.3) x 10^{22}
cm^{-2} and photon index Gamma = 1.0\pm0.2; it implies that the Chandra
point-source flux is virtually 100% pulsed. For a distance of 10 kpc, the X-ray
luminosity of PSR J2022+3842 is L_X(2-10 keV) = 7.0 x 10^{33} erg s^{-1}.
Despite being extraordinarily energetic, PSR J2022+3842 lacks a bright X-ray
wind nebula and has an unusually low conversion efficiency of spin-down power
to X-ray luminosity, L_X/Edot = 5.9 x 10^{-5}.Comment: 8 pages in emulateapj format. Minor changes (including a shortened
abstract) to reflect the version accepted for publicatio
RFI Identification and Mitigation Using Simultaneous Dual Station Observations
RFI mitigation is a critically important issue in radio astronomy using
existing instruments as well as in the development of next-generation radio
telescopes, such as the Square Kilometer Array (SKA). Most designs for the SKA
involve multiple stations with spacings of up to a few thousands of kilometers
and thus can exploit the drastically different RFI environments at different
stations. As demonstrator observations and analysis for SKA-like instruments,
and to develop RFI mitigation schemes that will be useful in the near term, we
recently conducted simultaneous observations with Arecibo Observatory and the
Green Bank Telescope (GBT). The observations were aimed at diagnosing RFI and
using the mostly uncorrelated RFI between the two sites to excise RFI from
several generic kinds of measurements such as giant pulses from Crab-like
pulsars and weak HI emission from galaxies in bands heavily contaminated by
RFI. This paper presents observations, analysis, and RFI identification and
excision procedures that are effective for both time series and spectroscopy
applications using multi-station data.Comment: 12 pages, 9 figures (4 in ps and 5 in jpg formats), Accepted for
publication in Radio Scienc
VLBI astrometry of PSR J2222-0137: a pulsar distance measured to 0.4% accuracy
The binary pulsar J2222-0137 is an enigmatic system containing a partially
recycled millisecond pulsar and a companion of unknown nature. Whilst the low
eccentricity of the system favors a white dwarf companion, an unusual double
neutron star system is also a possibility, and optical observations will be
able to distinguish between these possibilities. In order to allow the absolute
luminosity (or upper limit) of the companion object to be properly calibrated,
we undertook astrometric observations with the Very Long Baseline Array to
constrain the system distance via a measurement of annual geometric parallax.
With these observations, we measure the parallax of the J2222-0137 system to be
3.742 +0.013 -0.016 milliarcseconds, yielding a distance of 267.3 +1.2 -0.9 pc,
and measure the transverse velocity to be 57.1 +0.3 -0.2 km/s. Fixing these
parameters in the pulsar timing model made it possible to obtain a measurement
of Shapiro delay and hence the system inclination, which shows that the system
is nearly edge-on (sin i = 0.9985 +/- 0.0005). Furthermore, we were able to
detect the orbital motion of J2222-0137 in our VLBI observations and measure
the longitude of ascending node. The VLBI astrometry yields the most accurate
distance obtained for a radio pulsar to date, and is furthermore the most
accurate parallax for any radio source obtained at "low" radio frequencies
(below ~5 GHz, where the ionosphere dominates the error budget). Using the
astrometric results, we show the companion to J2222-0137 will be easily
detectable in deep optical observations if it is a white dwarf. Finally, we
discuss the implications of this measurement for future ultra-high-precision
astrometry, in particular in support of pulsar timing arrays.Comment: 22 pages, 7 figures, accepted for publication in Ap
A Survey of 56 Mid-latitude EGRET Error Boxes for Radio Pulsars
We have conducted a radio pulsar survey of 56 unidentified gamma-ray sources
from the 3rd EGRET catalog which are at intermediate Galactic latitudes (5 deg.
< |b| < 73 deg.). For each source, four interleaved 35-minute pointings were
made with the 13-beam, 1400-MHz multibeam receiver on the Parkes 64-m radio
telescope. This covered the 95% error box of each source at a limiting
sensitivity of about 0.2 mJy to pulsed radio emission for periods P > 10 ms and
dispersion measures < 50 pc cm-3. Roughly half of the unidentified gamma-ray
sources at |b| > 5 deg. with no proposed active galactic nucleus counterpart
were covered in this survey. We detected nine isolated pulsars and four
recycled binary pulsars, with three from each class being new. Timing
observations suggest that only one of the pulsars has a spin-down luminosity
which is even marginally consistent with the inferred luminosity of its
coincident EGRET source. Our results suggest that population models, which
include the Gould belt as a component, overestimate the number of isolated
pulsars among the mid-latitude Galactic gamma-ray sources and that it is
unlikely that Gould belt pulsars make up the majority of these sources.
However, the possibility of steep pulsar radio spectra and the confusion of
terrestrial radio interference with long-period pulsars (P > 200 ms) having
very low dispersion measures (< 10 pc cm-3, expected for sources at a distance
of less than about 1 kpc) prevent us from strongly ruling out this hypothesis.
Our results also do not support the hypothesis that millisecond pulsars make up
the majority of these sources. Non-pulsar source classes should therefore be
further investigated as possible counterparts to the unidentified EGRET sources
at intermediate Galactic latitudes.Comment: 24 pages, including 4 figures and 3 tables. Accepted for publication
in Ap
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